Most infants prefer liquid/food to be 98° F.+/−10° F. (36° C.+/−5.5° C.) which requires a heating method. Most heating methods are slow and can potentially overheat the contents leading to the possibility of scalding. In addition, microwave ovens are disfavored for warming breast milk due to potential nutrient loss and lack of precise temperature control.
The principles of thermal energy storage in phase-change materials are known. A salt solution may be “supersaturated”, i.e. containing more than the equilibrium amount of dissolved solute at a specific temperature. A typical salt used is a solution of sodium acetate trihydrate (NaC2H3O2-3H2O). The sodium acetate trihydrate can also be a “supercooled” solution, where it is cooled below its freezing point without transforming into a solid. Sodium acetate has a freezing point of 131° F. (54° C.), but can easily exist as a supercooled liquid at room temperature. The supersaturated, supercooled solution of sodium acetate is unstable and will crystallize if a seed crystal is present or a disturbance causes initiation of crystallization. This crystallization to a solid is exothermic, meaning it releases heat. The transition of sodium acetate trihydrate to solid form rapidly warms the salt solution, up to a maximum of approximately 54° C. (131° F.). It will stay at approximately this temperature until all of the sodium acetate has crystallized and the stored chemical energy has been completely converted to thermal energy. The energy so released may be put to practical use in many ways.
The solution used for phase-change heat packs is typically sodium acetate trihydrate which has the advantage of being food safe, FDA approved, and widely available. Other salts known to exhibit similar behavior but with differing melt points, include: sodium sulfate decahydrate (Na2SO4-0H2O), sodium thiosulfate pentahydrate (Na2S2O3-5H2O), sodium chromate decahydrate (Na2CrO4-10H2O), calcium chloride hexahydrate (CaCl2-6H2O), magnesium chloride hexahydrate (MgCl2-6H2O), magnesium nitrate phosphate dodecahydrate (Mg2(NO3)(PO4)-12H2O), calcium nitrate trihydrate (Ca(NO3)2.3H2O), and trimethylol ethane hydrate (C5H12O3.H2O), among others, will function in essentially the same manner.
Supersaturation is achieved by first heating a solution of salt in water to above the crystal melt point, thereby allowing the ions to completely dissociate their bonds and dissolve in the water, then cooling the solution. For example, the melt point for sodium acetate trihydrate is 54° C. (131° F.). Supersaturation can be achieved by heating a solution of sodium acetate trihydrate to at least 54° C. (131° F.) until all crystals are dissolved, then cooling the solution to room temperature (approximately 20° C. or 68° F.).
Crystallization can be induced by introducing a crystal nucleus at a temperature below melt point, or by creating a crystal nucleus by compressing a small portion of solution in a trigger to induce crystallization, which then cascades throughout the solution. This crystallization is an exothermic process at room temperature, and the heat given off can be used as a heat source, such as for heating food. After the solution has crystallized the supersaturated solution can be regenerated by reheating the solution to above melt point, until the crystals completely dissolve, and then allowing the solution to cool again. The supersaturated solution remains dissolved and will not spontaneously nucleate even at normal refrigerator temperatures of (1-3° C.) 33-38° F., unless initiated by a trigger or nucleate crystal.
The maximum temperature is self-limited by the maximum temperature of the salt solution undergoing crystallization. For example, a typical supersaturated solution of sodium acetate trihydrate reaches a maximum temperature of approximately 54° C. (131° F.) when triggered from room temperature. This heat energy can be transferred to food within a container through the walls of a heating element within the container.
The precise mechanism causing nucleation by compression is not clearly understood but it is believed that the pressure disturbance causes some of the molecules to flip to the solid crystal state thereby providing seeds for cascading crystallization. Metallic mechanisms can be used to induce crystal nucleation, but metallic mechanisms have the disadvantage of not being microwave safe. Ceramics are microwave safe, but not all ceramics are reliable in generating crystal nuclei through compression. Applicants have determined through experimentation that steatite, a crystalline form of magnesium silicates such as (Mg3Si4O10(OH)2), which is commonly used as an insulating material in electrical components, is reliable and effective in initiating nucleation. Nucleation may be induced by compressing two pieces of steatite together, or by compressing a single steatite element against another hard material such as ceramic, metal, or hard plastic. The specific shape of the steatite element is not critical, so a shape convenient to manufacture can be used.
Not all ceramics are reliable in initiating crystallization by compression. Materials found not to be reliable were: aluminum silicate, alumina at 96% aluminum oxide, alumina at 99% aluminum oxide, cordierite (magnesium aluminum silicate), silicon carbide, titanate (titanium dioxide), zirconia (zirconium dioxide), porcelain (kaolinite), alumina silicate, mullite (alumina silicate lava), quartz/silica, wollastonite (calcium magnesium silicate), borosilicate glass (e.g. Pyrex™ from Corning, Inc.), silicon nitride, boron nitride, glass ceramic, mica/borosilicate (Macor™ from Corning, Inc.), stoneware, and Material 10.90 (a ceramic material from Associated Ceramics and Technology, part number 724-353-1585).
Heating devices using this heat released by supersaturated salt solutions transforming from the dissolved state to crystalline or frozen when occurring below their freezing point are known. Recharging these devices by heating them using an external heat source or microwaves is also known. However, existing devices do not provide safe, effective, and convenient means for using supersaturated salts to heat food such as in a baby bottle or thermos, using an accessible but protected and reliable trigger devices, and which can be recharged and reused indefinitely.
The following represents a list of known related art:
Date ofReference:Issued to:Issue/Publication:U.S. Pat App 2005/0145242 A1RomeuPublished Jul. 7, 2005U.S. Pat. No. 4,983,798Eckler et alJan. 8, 1991U.S. Pat. No. 6,410,896Witonsky et alJun. 25, 2002U.S. Pat. No. 6,708,883 B2KolbMar. 23, 2004U.S. Pat. No. 6,123,065TeglbjargSep. 16, 2000U.S. Pat. No. 6,079,405JustoJun. 27, 2000U.S. Pat. No. 4,880,953MankerNov. 14, 1989U.S. Pat. No. 5,275,156Milligan, et al.Jan. 4, 1994U.S. Pat. No. 4,460,546Kapralis, et al.Jul. 17, 1984U.S. Pat. No. 4,899,727Kapralis, et al.Feb. 13, 1990U.S. Pat. No. 4,580,547Kapralis, et al.Apr. 8, 1986U.S. Pat. No. 5,056,589Hettel, et al.Oct. 15, 1991U.S. Pat. No. 5,143,048Cheney, IIISep. 1, 1992U.S. Pat. No. 4,860,729Benson, et al.Aug. 29, 1989
The teachings of each of the above-listed citations (which does not itself incorporate essential material by reference) are herein incorporated by reference. None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed.
U.S. Pat. App. 2005/0145242 A1 to Romeu discloses an autothermic packaging food container, which has separate compartments to contain the chemicals prior to reaction, is not reusable. U.S. Pat. No. 6,708,883 to Kolb discloses an infant nipple attachment which is disposable and not reusable. U.S. Pat. No. 6,123,065 to Teglbjarg discloses a feeding bottle which heats with the mixing of two chemicals, which limits the heating unit as disposable and not rechargeable. U.S. Pat. No. 6,079,405 to Justo discloses a dual food product mixing container that utilizes two chambers required to mix chemicals for heating which limits the unit to a single use.
U.S. Pat. No. 4,983,798 to Eckler, et al, discloses a method of using organic solids exhibiting meso-crystalline transition temperatures within a range of 30-200° C. to maintain warm foods warm. Eckler however, does not discuss using supersaturated salt solutions. Nor does Eckler disclose apparatus or methods which are stable at room temperature or refrigeration temperatures for an indefinite period and then activated for use only at the desired time. Eckler requires the heating apparatus to be pre-heated, and then this apparatus merely retains this heat for a prolonged period through the meso-crystalline phase-transition process. Thus it lacks the advantages of indefinite storage in a ready-to-use condition and activation only when desired by the user.
U.S. Pat. No. 4,880,953 to Manker, discloses a method of recharging a heat pack by microwave energy where the flexible pack must have no “welds” to trap solution and cause “hot-spotting”. However, Manker only teaches metallic spring-type activators floating freely within a seamless flexible pack. Manker would therefore not be usable within a bottle or food container because the pack is not rigid and the trigger mechanism would be inaccessible. Manker does not disclose interchangeable rechargeable heating elements insertable into bottles, nor portable recharging devices.
U.S. Pat. No. 5,275,156 to Milligan, et al., discloses a trigger device that floats free in a supercooled salt solution which is activated by applying pressure to the device. This device has the same disadvantages as Manker. The device in Milligan is also susceptible to inadvertent activation if agitated, because the solid objects in the trigger are free to contact each other when jostled.
U.S. Pat. Nos. 4,460,546, 4,899,727 and 4,580,547 to Kapralis, et al., disclose the use of another set of trigger devices which float free in the supercooled salt solution or which use metallic discs (generally, Kapralis, et al., disclose concave discs which are caused to “snap” in order to activate the heat pack). Kapralis does not disclose the ability to regenerate the heating device, nor does Kapralis disclose use of ceramic materials. Kapralis does not disclose a device susceptible to use with food containers or bottles, and does not disclose a portable regenerator.
U.S. Pat. No. 5,056,589 to Hettel, et al., discloses only the use of metallic spring mechanism free floating in a flexible pouch for crystallizing a supercooled salt solution. U.S. Pat. No. 5,143,048 to Cheney, III, describes a trigger device which requires breaking an ampoule or disk to initiate a chemical catalyst, and is therefore not rechargeable or reusable.
U.S. Pat. No. 4,860,729 to Benson, et al, discloses a trigger device which traps a crystallite of the material between two solid objects and retains it there by pressing the objects together with enough force to create sufficient pressure to keep the crystallite isolated between the two solid objects when it is immersed in the phase-change material to keep it from melting. This has the disadvantage that the trigger must be specifically prepared prior to regeneration and requires complex apparatus to achieve. In addition, the trigger is susceptible to inadvertent activation if disturbed, as a crystal nucleus is always present and liable to trigger crystallization if liquid leaks into the retaining area or the pressure is relieved slightly. Nor does Benson disclose non-metallic apparatus, or a portable recharging devices.
U.S. Pat. No. 6,410,896 to Witonsky, et al, discloses use of liquid crystal temperature indicators in conjunction with devices for distributing microwave evenly throughout a liquid filled bottle for heating. Witonsky, however, does not discuss using rechargeable heating elements using supersaturated salt solutions.
Still other features would be desirable. For example, a system whereby rechargeable heating elements could be easily recharged in an automobile or hotels during long trips would be useful. Heating elements which are easily carried and can be quickly and easily exchanged using purpose designed or standard food containers would be advantageous.
Thus, while the foregoing body of art indicates it to be well known to have a heating element using supersaturated salts, the art described above does not teach or suggest a food container or baby bottle which has the following combination of desirable features: (1) reusable; (2) rechargeable in a microwave oven; (3) dishwasher and food safe; (4) may be interchangeable; (5) may include a temperature indicator; (6) won't harm breast milk (as can happen with a microwave) or baby formula; (7) usable with a portable recharger compatible with automobile auxiliary outlets; (8) can be stored in a refrigerator; and, (9) is protected from inadvertent activation.
Additional advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. Further benefits and advantages of the embodiments of the invention will become apparent from consideration of the following detailed description given with reference to the accompanying drawings, which specify and show preferred embodiments of the present invention.